Angiotensin II has been shown to stimulate protaglandin E production and elevate cGMP levels in continuous cell culture lines of vascular endothelial cells indicating that vascular endothelial cells do not merely provide an inert lining for the vasculature but are actively involved in the physiological response of the vasculature to vasoactive hormones. The overall goal of this proposal is to: (1) characterize biochemiccally the angiotensin II receptors of rat aortic endothelial cells and (2) determine if differences exist between angiotensin II receptors of endothelial cells from normal and spontaneously hypertensive rats which may play a role in essential hypertension in man. To accomplish these goals, primary cultures and continuous cell culture lines of aortic endothelial cells from normal and spontaneously hypertensive rats will be established and characterized for specific markers of differentiated endothelial cells. 125I-labeled angiotensin II with a high specific activity (approximately 1000 micro Ci/micro g) will be used to quantitate the number and binding affinity of angiotensin II receptors of the cultured endothelial cells. If endothelial cells from spontaneously hypertensive rats contain more receptors or have a higher binding affinity for angiotensin II, this may relate to the maintenance of elevated blood pressures found in rats (and humans) with normal serum levels of angiotensin II. The hormonal regulation of angiotensin II receptor will be investigated by exposing cultures to various hormones and measuring the "up or down regulation" of angiotensin II receptor. A tritium labeled photoactivated arylazide derivative or angiotensin II will be used to covalently label the receptor which will be identified and characterized using SDS polyacrylamide gel electrophoresis. A ferritin-angiotensin-II probe will be used to map the topographical distribution of angiotensin II receptors. These experiments will add to our knowledge of the interaction of angiotensin II with vascular endothelial cells and may suggest the possible roles of angiotensin II and endothelial cells in essential hypertension in man.